1. Field of the Invention
The present invention relates to telephony. More particularly, the present invention relates to speakerphones that have a wireless connection to their microphone.
2. Description of Related Art
Telephones equipped with a loud speaker and microphone (xe2x80x9cspeakerphonesxe2x80x9d) allow one or more talkers in a room with the speakerphone to participate in a telephone conversation without using their hands. Freeing the hands during telephone conversations has many advantages, including facilitating note-taking, decreasing neck, arm, and shoulder fatigue, and allowing the talker to freely move about the room.
Speakerphones may be designed to operate in either half-duplex or full-duplex mode. In the half-duplex mode, when conducting a telephone call using a speakerphone, only one party involved in the telephone call can have his voice transmitted at one time. If both parties try to speak simultaneously, a choppy sound effect known as clipping results. Having to speak in turn can be unnatural and can make conversation difficult and laborious. Thus, many speakerphones are designed to operate in full-duplex mode. The full-duplex mode allows incoming and outgoing parties"" voices to be simultaneously transmitted so that there is no clipping or choppyness. This results in much more natural and spontaneous flowing conversation. Full-duplex is even more important when more than one person is in a room using the speakerphone for a conference call. It can be difficult for the person on the other end of the conference call, connected via the telephone network, to break into the ongoing conversation. In addition, noise or commentary in the conference room can cut off the person on the other end.
FIG. 1 shows a conventional full-duplex speakerphone 100. The speakerphone 100 includes a base station 102 and a handset 104 that is connected to the base station 102 by a cable 105. The base station 102 includes a keypad 106, a speaker 108, and a microphone 110. A person using the speakerphone 100 can conduct a telephonic conversation with another person by using the handset 104 to speak and hear, or by using the speaker 108 to hear the other person and the microphone 110 to speak.
However, conventional full-duplex speakerphones like the one shown in FIG. 1 operate under severe constraints that adversely effect the audio quality of the telephonic conversation. The speaker 108 and microphone 110 are both located in the base station 102, in close proximity to one another. The close proximity results in acoustic coupling between the speaker 108 and microphone 110 by which sound emanating from the speaker 108 is picked-up by the microphone 110. This causes an echo signal to be transmitted by the speakerphone 100 to a listener connected to the speakerphone 100 over the telephone network.
This effect becomes more pronounced when the room talker is much farther from the microphone 110 than the speaker 108. The microphone 110 receives the speaker 108 signal as a very loud signal, while the voice of the distant room talker is received by the microphone 110 as a very quiet signal. Moreover, the room talker""s voice will typically echo as a result of impedance mismatches in the telephone network, from the point where the speakerphone 100 is connected to the telephone network to the termination at a central office of the telephone service provider. To mitigate these echoes, full-duplex speakerphones have echo cancelers. While echo cancelers can reduce the echo, they do not fully cancel the echo, leaving residual echos. When the residual echoes are audible, this significantly degrades the quality of a conversation.
In addition, full-duplex speakerphones like that illustrated in FIG. 1 tend to pick-up substantial amounts of unwanted noise. With the microphone 108 fixed in the base station 102, the person talking may be a significant distance from the microphone 108. The farther away the talker is from the microphone 108, the more difficult it becomes to hear the talker""s voice. To make the talker audible, the microphone signal must be amplified. But this also amplifies the system background noise, which includes the residual echo, quantization noise in digital systems, environmental background noise, and the noise floor of the microphone 108. The more noise the microphone 108 picks-up, the greater the degradation in sound quality during the call.
FIG. 2 shows a full-duplex speakerphone 200 that is designed to reduce the acoustic coupling problem. The speakerphone 200 includes a speaker 202 and microphone 204. The speakerphone 200 has a line side 206, which is connected on one end to the public switched telephone network (PSTN) 208, and a room side 210. The speakerphone 200 also has a transmit signal path 212 and a receive signal path 214. A line echo canceler (LEC) 216 is located between the transmit signal path 212 and receive signal path 214 on the line side 206, and an acoustic echo canceler (AEC) 218 is located between the transmit path 212 and receive path 214 on the room side 210.
A line talker signal 220 incoming to the speakerphone 200 from the PSTN 208 is converted from analog to digital form, and any line echo 221 excited by the LEC reference input signal (LECref) 222 that is estimated by the LEC 216 is subtracted from the LEC echo input signal (LECecho) 224. A residual line signal 226, which ideally contains only the line talker signal 220, is then amplified by the receive automatic gain control (AGC) 228, which is designed to maintain its output power at a specified level. The receive AGC 228 outputs a signal that is converted into an analog form and output to the speaker 202, completing the receive signal path 214.
Similarly, in the transmit direction, the microphone 204 picks-up a room talker signal 232, which is converted into an AEC echo input signal (AECecho) 234. The room echo 236, as estimated by the AEC 218, is then subtracted from the AECecho signal 234, and the residual transmit signal 238, which ideally contains only the room talker signal 232, is amplified by the transmit AGC 240 to a specified level. The amplified signal is then converted to analog and output to the PSTN 208, completing the transmit signal path 212.
In practice, however, the AEC 218 and LEC 216 do not provide perfect cancellation, and the transmit and receive signals leak into one another. As a result, a potential loop exists in the signal path, shown by gain loop 242. The AGCs 228, 240 and other analog or digital gains may, at some frequencies, cause gain around the loop 242 to be greater than unity, especially if the standard deviations of the input line 244 and/or room talker signal 232 are small, and the gains of the AGCs 228, 240 are high. When the loop gain 242 is greater than unity at any frequency, the full-duplex speakerphone 200 is prone to oscillate or feed-back.
To correct these problems, expensive circuitry and software must be designed and provided in the full-duplex speakerphone 200. Even with the added circuitry and software, the speakerphone 200 may experience feedback due to the close proximity of the speaker 202 and microphone 204 and resultant acoustic coupling between them.
FIG. 3 shows another type of speakerphone 300 that is designed to provide a reduction in acoustic coupling and feedback. The speakerphone 300 has a base station 302, keypad 304, speaker 306, and base station microphone 308. Speakerphone 300 also includes a remote microphone housing 312, which is connected to the base station 302 by a cable 310. The remote microphone housing 312 has a remote microphone 314. Locating the remote microphone 314 remote from the speaker 306 reduces coupling between the remote microphone 314 and speaker 306.
The use of cable 310 to connect the remote microphone housing 312 to the base station 302, however, limits the flexibility of the speakerphone 300. Cable 310 physically limits where the remote microphone 314 can be located relative to the base station 302 and talker. If the talker were to try to relocate the microphone housing 312 around the room to reduce the background noise problem, the cable 310 would physically limit the talker""s mobility and could also become entangled with furniture and other persons present in the room.
Accordingly, a need exists for an inexpensive speakerphone that reduces background noise, reduces acoustic coupling and resultant feedback, and provides flexibility and ease of use. The present invention provides such a speakerphone.
The present invention is a full-duplex speakerphone that is coupled to a network. As used herein, the network may be any type of network that is capable of carrying a telephony signal, including the public switched telephone network (PSTN), a private telephone network, a cellular telephone network, a paging network, or a computer network such as the Internet. These exemplary networks are not to be considered limiting, however, as the speakerphone of the present invention may be designed to work with any telephonic or computer network or system.
In a first embodiment, the invention is a full-duplex speakerphone that is coupled to a network. The speakerphone includes a base station having a network connection, a speaker, and a wireless receiver. The base station receives a first network signal from the network, and the speaker delivers an audible signal derived from the first network signal. The speakerphone also includes a wireless remote microphone apparatus having a microphone and a wireless transmitter. The microphone receives an audio signal, and the wireless transmitter transmits the audio signal over the air to the wireless receiver in the base station. The base station converts the audio signal into a second network signal and sends the second network signal to the network. The base station and wireless remote microphone apparatus operate in full-duplex mode.
In a second embodiment, the present invention is a full-duplex speakerphone that is coupled to a network. As in the preceding embodiment, this second embodiment includes a base station and a wireless remote microphone that operate in full-duplex.
The base station of the second embodiment includes a network connection, a speaker, a wireless receiver, a first signal converter coupled to the network, a line echo canceler coupled to the first signal converter, a compressor coupled to the line echo canceler, a decompressor coupled to the compressor, a second signal converter coupled to the compressor and the speaker, and a wireless transmitter coupled to the compressor. The first signal converter converts an analog line signal received from the network into a digital line signal, and the line echo canceler reduces an echo component of the digital line signal to obtain a residual digital line signal. The compressor compresses the residual digital line signal into a compressed digital line signal, and the decompressor decompresses the compressed residual digital line signal into a decompressed digital line signal. The second signal converter converts the decompressed digital line signal into a speaker signal, and the speaker audibly outputs the speaker signal. The wireless transmitter sends a transmit signal derived from the compressed digital line signal over the air to the wireless remote microphone apparatus to be used as a reference signal.
The wireless remote microphone of the second embodiment has a microphone and a wireless transmitter. The microphone receives an audio signal, and the wireless transmitter transmits the audio signal over the air to the wireless receiver in the base station, the base station converting the audio signal into a network signal and sending the network signal to the network.
In a third embodiment, the invention is a full-duplex speakerphone that is coupled to a network. The speakerphone includes a base station and a wireless remote microphone that operate in full-duplex mode.
The base station of the third embodiment includes a speaker, a wireless receiver, a first signal converter coupled to the network, a line echo canceler coupled to the first signal converter, an acoustic echo canceler coupled to the line echo canceler and to the wireless receiver, and a second signal converter coupled to the acoustic echo canceler and to the speaker. The first signal converter converts an analog line signal received from the network into a digital line signal, and the line echo canceler reduces an echo component of the digital line signal to obtain a residual digital line signal. The second signal converter converts the residual digital line signal into a speaker signal, and the speaker audibly outputs the speaker signal.
The wireless remote microphone of the third embodiment includes a microphone and a wireless transmitter. The microphone receives an audio signal, and the wireless transmitter transmits the audio signal over the air to the wireless receiver in the base station. The acoustic echo canceler reduces an echo component of the audio signal to obtain a residual audio signal, and the base station converts the residual audio signal into a network signal and sends the network signal to the network.